1. Field of the Invention
The present invention relates to an apparatus for adjusting a pressing force of a wiper for wiping a window face of a vehicle such as an automobile.
2. Description of the Related Art
In general, a conventional wiper of this type presents such a defect that when a velocity at which a vehicle travels increases, a wiper blade floats due to a dynamic lift caused by air flow about the vehicle, resulting in a decline in wiping capability of the wiper. For the purpose of preventing such a decline in wiping capability during high-speed travelling, a biasing force of a spring for pressing the wiper blade against the window face is adjusted in association with a motor drive. There have been proposed a variety of means for preserving the wiping capability of the wiper blade during high-speed travelling. Even if these means are based on the motor drive, however, they do not fulfill the requirement that the biasing force of the spring be varied instantaneously, and it follows that the variations in biasing force take much time. In the meantime, the wiper blade remains in a state where the original wiping capability is degraded.